Displaying video content originally created for television on a computer display is a desired feature for a multi-media computer system. However, television video signals and the computer video differ in formats. For example, many television and video signals are interlaced, where a set of scan lines of a single video frame are not scanned or transmitted sequentially. A typical U.S. NTSC (National Television System Committee) television signal uses two fields for each frame. Each field contains video data for every other horizontal line of the entire frame. Consecutive scans of the two fields occur 30 times per second. The scan lines for one field are transmitted first, followed by the scan lines of the second field. The viewer perceives the resulting image (or frame) as a blend of the two individual fields with an effective refresh rate of 60 Hz. The interlaced format reduces flicker without doubling of the data transfer rate which would be needed to update the entire frame at 60 Hz.
In contrast, computer monitors are not interlaced. Computer monitors sequentially scan the entire display area, one scan line after another (typically referred to as progressive scan). To display an interlaced scanned sequence, such as a video signal, on such progressively scanned devices, a deinterlacing process converts each separate field into a complete display frame that can be sequentially presented to the display device. The main task of a de-interlacing process is to reconstruct the missing line between each of the scan lines of an interlaced field. An entire frame is scanned line-by-line, typically from top to bottom. The process repeats and re-scans the entire frame at a given refresh rate, for example, 60 Hz.
There are two primary conventional de-interlacing methods, each with their own strengths and weaknesses. “Inter-field” techniques simply merge the data from the second field with the data from the first field to produce a completed frame. If there is no motion in the video frame, such methods yield an ideal reconstituted picture. Vertical resolution can be as good as an original noninterlaced frame. However, if there is motion within the video signal, motion effects will generally be visible to the human eye. Motion effects arise when an object, which was in one location during the scanning of the first field, has moved when the alternating scan lines of the second field are scanned. Simply combining the interlaced scan lines of the two fields yields an unacceptable rendition of the object.
“Intra-field” techniques use data only from a single field to produce a complete frame. Such methods are better suited for video frames having motion. With an intra-field technique, the values for non-existent pixels are interpolated from pixel values in the scan lines above and below the non-existent pixels. The intra-field technique produces no deleterious motion effect, since motion is not incorporated from one field to the next. However, the intra-field technique also does not enhance vertical resolution, since the intra-field technique merely interpolates from existing pixel values within a single field and does not use pixel information for missing scan lines from the second field. Also, simple intra-field deinterlacing techniques (such as simple vertical interpolation) tend to generate unacceptable jagged pictures along diagonal edges.
U.S. Pat. No. 6,421,090 to Jiang, et al. entitled “Motion and edge adaptive deinterlacing” shows a method for interpolating a pixel during the deinterlacing of a video signal, the video signal including at least two fields of interlaced scan lines, each scan line including a series of pixels having respective intensity values. This method includes generating a motion value representative of the motion between successive frames about the pixel, detecting an edge direction about the pixel, performing an edge adaptive interpolation at the pixel, using the detected edge direction, and performing a motion adaptive interpolation at the pixel, using the generated motion value. The corresponding apparatus for interpolating a pixel during the deinterlacing of a video signal includes a motion value generator configured to generate a motion value representative of the motion between successive frames about the pixel, an edge direction detector configured to detect an edge direction about the pixel, an edge adaptive interpolator configured to perform an edge adaptive interpolation at the pixel, using the detected edge direction, and a motion adaptive interpolator configured to perform a motion adaptive interpolation at the pixel, using the generated motion value.
U.S. Pat. No. 6,459,455 to Jiang, et al. entitled “Motion adaptive deinterlacing” relates to a method and apparatus for deinterlacing video frames. The method and apparatus for deinterlacing video frames selects a location for deinterlacing and measures motion at that location. A deinterlacing method is selected based on the measured motion and a pixel value is created for the location.